This invention relates generally to multi-layer injection molding apparatus and more particularly to such apparatus having integral multi-layer melt dividing bushings seated in the melt distribution manifold for dividing the melt flowing to annular melt channels in the heated nozzles.
Injection molding apparatus for making multi-layered protective containers for food or preforms or parisons for beverage bottles are well known. Often the inner and outer layers are made of a polyethylene terephthalate (PET) type material with one or more barrier layers made of a material such as ethylene vinyl alcohol copolymer (EVOH) or nylon. In some multi-cavity apparatus the two different melts are distributed through a single melt distribution manifold having different passages, but preferably for materials such as these having different injection temperatures of about 565.degree. F. and 400.degree. F. respectively, the two melts are distributed through two different melt distribution manifolds. In some cases, the melts are injected sequentially, while in other cases both coinjection and sequential injection are utilized. The two materials are injected through a heated nozzle having a central melt channel and one or more annular melt channels extending around the central melt channel to a gate leading to the cavity.
It is also known to divide the melt flowing to the annular melt channel to provide more uniform distribution around the annular melt channel. As seen in the applicant's U.S. Pat. No. 5,094,603 which issued Mar. 10, 1992, this has been done by providing a single layer melt distribution plate mounted between the rear end of the heated nozzles and the front face of the melt distribution manifold. While this is suitable for many situations, it has the disadvantage of requiring extensive machining of the front face of the melt distribution manifold and the rear ends of the heated nozzles. Also, it is not suitable for receiving melt from two separate manifolds and has the disadvantage of increasing the height of the mold.